Field of the Invention
This invention relates to antithrombogenic and lubricious medical instruments such as catheters and guidewires useful, e.g. in angiography.
Contacting blood with a foreign object having a plastic or metal surface induces a complex set of clot-forming reactions that occur at the blood surface interface. Thromboembolism is a major complication associated with the clinical use of artificial devices, such as catheters, guidewires, mechanical heart valves, ventricular assist devices, implantable artificial hearts, vascular grafts, etc. In particular, thromboembolism is an important complication of angiographic procedures, particularly with catheter and guidewire manipulations proximal to the brachiocephalic vessels.
Angiographic guidewires are known to be thrombogenic. If a stainless steel or teflon-coated guidewire is exposed to streaming arterial blood in dogs, they are covered by a fibrin sheath within several minutes. It has been suggested that this high degree of thrombogenicity may also be related to the corrugated shape of the guidewires which probably induces turbulence between each wire coil, facilitating platelet adherence. Teflon.RTM. coatings on guidewires, however, offer insufficient protection from thrombogenesis.
Certain agents, for example, heparin, on a foreign surface can inhibit clot formation. Frech et al., in "A Simple Noninvasive Technique to Test Nonthrombogenic Surfaces," The American Journal of Roentgenology Radium Therapy and Nuclear Medicine, Vol. 113, 1971, P. 765 discloses coating of a guidewire with a benzalkonium-heparin complex. Ovitt et al., in "Guidewire Thrombogenicity and Its Reduction" Radiology, reports Teflon.RTM.-coated guidewires treated with benzalkonium-heparin. Williams U.S. Pat. No. 4,349,467 applies heparin to solid polymeric resin substrates by steeping the substrate in a solution of an ammonium salt and contacting the substrate with a heparin salt solution.
It is also desirable to provide a highly lubricious coating to medical instruments and especially to those instruments that must pass through narrow, tortuous body passages. It has been shown that water soluble polymers which are swellable with water but do not dissolve have very low coefficients of friction when wet, even lower than that of Teflon.RTM. (polytetra fluorethylene).